Mining the crash area strikes me as indicative of low rung actors running the show without any oversight.
The grunts might like the idea of mining the area, as they know that the people who have been shooting at them will be effected; however, a more strategic thinking staff would cancel that plan based on the PR damage.
That said, we are dealing with Russians and they might not care, thinking that they can just deny that they did it and leave it up to the propaganda organs to fight out the strategy.
Plundering troops have been the norm since the beginning of wars. Plunder is the bonus to the troops for winning.
To judge the world in the light of progress since WW II is error.
There should be missile fragments amongst the ruins. Their discovery would yield what missile it was and likely where and when it was manufactured. There is therefore a very strong incentive for the perpetrators to not to allow independent inspection of the wreckage.